This invention relates to the construction of a magneto-resistive head and in particular to the construction of a magnetic head for applying a bias magnetic field to a magneto-resistive film with a high efficiency.
Recently, magnetic heads (hereinbelow abbreviated to MR head) utilizing magneto-resistive film (hereinbelow abbreviated to MR film) have been used more and more widely. The reproduction output of the MR heads does not depend on the relative velocity between recording media and magnetic heads, and in particular a sensitivity higher than that of a conventional inductive head is expected at low velocities. A constant magnetic field is applied to the MR head from the exterior in order to improve the sensitivity and the linearity of the magneto-resistive effect. This magnetic field is called bias magnetic field. A number of methods for realizing it have been improved, such as (1) a method, by which a permanent magnet is located in the proximity of the MR film, (2) a method, by which a conductive film is placed in contact with the MR film, (3) a method, by which a soft magnetic film is located in the proximity of the MR film, etc. (cf. i.e. J. Appl. Phys. 55(6), Mar. 15, 1984 pp. 2226-2231 "Magnetics of small magneto-resistive sensors").
FIG. 1 illustrates a general construction of an MR head and FIG. 2 is its cross-sectional view. It is well-known that in the MR head two shield members 4 and 4' are, in order to increase its spatial resolution, disposed so that an MR film 1, a bias film 2 and an insulating film 3 are interposed therebetween, as indicated in the cross-sectional view of FIG. 2. At this time the axis of easy magnetization of the MR film 1 is oriented in the direction of the track width (M direction). In order to increase the sensitivity and the linearity of the MR film, the magnetization is previously oriented by the bias film 2 e.g. in an M' direction. In such a state, the MR head receives the signal magnetic field produced by the medium magnetization 15 on a recording medium 10 and detects variations in resistance of the MR film due to variations in inclination of the magnetization as signals.
When the bias means described previously are applied to the device indicated in FIG. 1, method (1) lacks the linearity, although it has a high sensitivity, and the sensitivity of method (2) is low, because the conductive film for bias short-circuits the MR film. The soft magnetic film bias indicated in method (3) has both a high sensitivity and a good linearity. However, heretofore, no consideration has been given to the thickness, magnetic characteristic, etc. of the MR film and the soft magnetic film for bias.